The present invention relates to a device for the mounting of very wide-band microwave monolithic integrated circuits, notably GaAs circuits.
Wide-band microwave monolithic integrated circuits such as GaAs circuits are much used in equipment that has to work in very wide bands, for example of 2 to 20 GHz or more. GaAs circuits improve performance characteristics notably because of the uniformity of the gain obtained, and they enable a diminution of volume and a reduction of the batch production prices. These advantages are further accentuated in very wide passband applications by the use of the distributed amplifiers technique, providing simultaneously for high gain, a very wide band, low reflection coefficients at input and at output, and efficient input/output insulation.
However, these integrated circuits should be provided with circuits for the isolation or decoupling of the supply or bias circuits. Now, these decoupling circuits use capacitors to decouple the supplies used to bias the amplifiers, and the lower the frequencies at which it is sought to work, the greater should be the capacitance value of these capacitors (and hence the greater should be their size). These capacitors therefore take up a great deal of semiconductor surface area, thus preventing as great a reduction in cost and in space requirements as might have been hoped for. In practice, it is not sought to achieve decoupling at frequencies below 5 GHz so as not to excessive penalize the size of these chips and manufacturing output, for the manufacturing output levels of capacitors made in thin layers are not very great.
If it is sought to work at lower frequencies than 5 GHz, in the case of very wide band applications, then a known approach consists in complementing the decoupling with very external capacitors of very high capacitance value made on an attached support bearing the integrated circuits. This support may be a metal support with attached capacitors or a conductive silicon support on which MOS (metal-oxide-semiconductor) capacitors are made.
A drawback of this approach is, however, the appearance of a resonance due to a capacitor on integrated circuit/linking wire/external capacitor system. It is practically not possible to diminish the resonance frequency for this would imply an excessively high value of capacitance on integrated circuit and a very high inductance of the connecting wire, hence an excessive space requirement and problems of parasitic modes for a long connecting wire.